Antimicrobial resistance is a growing concern worldwide, and the severity of the situation is compounded by the modest pipeline of new antimicrobial products. Many strains of medically important bacteria have become increasingly resistant to antibiotics used in the treatment of clinical infections. This problem will continue to worsen over time, unless new antibiotics are developed soon. Preliminary characterization of mutacin 1140, an antibiotic made by a strain of Streptococcus mutans, suggests that it holds great promise. It is a member of the small, novel class of antibiotics called lantibiotics. It is bactericidal at low concentrations against all Gram positive bacteria which it has been tested, including multidrug resistant Staphylococcus aureus and Enterococcus faecalis. It is also active against some Gram negative pathogens. Among other features that make mutacin 1140 desirable for use as an antibiotic, is that spontaneous mutations to resistance have not been found among several pathogens tested. A novel mechanism of activity for mutacin has been described, in which it binds to lipid II trapping lipid II in a large complex of mutacin monomers that abduct lipid II from bacterial growth zones. These growth zones occur at the site of cell division where lipid II carries the peptidoglycan subunits required for the synthesis of new cell wall. The three dimensional structure of mutacin 1140 has been solved by our group providing an opportunity to make "intellectual choices" for site-directed mutagenesis. Thus the goal of this application is to identify the structural components of the antibiotic that are important for lipid II binding, complex formation, and their associated functions with the post-translational modification machinery. Of interest, would be the design of analogs that contain lipid II binding capability, but have lost the ability to form complexes, as well as analogs that can form complexes, but have lost the ability to bind to lipid II. These types of analogs would further our understanding of the mechanism of activity of mutacin 1140 as it pertains to specific regions in the antibiotic. Each mutant will be scored in this proposal, as they relate to lipid II binding, complex formation, bactericidal activity, and their associated function with the modification machinery. PUBLIC HEALTH RELEVANCE The proposal addresses the need for furthering our understanding of the function of an antimicrobial compound called mutacin 1140. A better understanding of the function of the structural elements of this antibiotic may aid in the development of a new class of antibiotics. [unreadable] [unreadable] [unreadable]